The present invention relates to a method for producing multifilament yarns from thermoplastic polymers by spinning individual filaments from a plastic in molten condition, the filaments after being formed in the spinning nozzles of one or more spinning heads and, after issuing from the nozzles, being subjected to subsequent preorientation, solidification, grouping into a multifilament bundle, and preparation during delivery and before being deposited or wound onto bobbins, or further processing.
In a paper entitled "Neues Spinnverfahren zur Herstellung texturierter Garne aus Polyester" [New Spinning Process for Producing Texturized Polyester Yarns] by H. Schatzle, published in Chemiefasern/Textil-Industrie [Chemical Fibers/Textile Industry] in April 1973, at pages 295/296, an overview is given of the developments in this field. In this connection the conventional process, spin stretching, stretch texturizing, and rapid, or stretch, spinning are discussed. Recent developments in the production of polyester yarns have led to the attainment of production speeds of 3,500 to 4,000 m/min, which also constitute the optimum speed for other thermoplastic polymers, such as, for example, polyamide 6.6.
A particular problem presented by such high speeds is that the yarn tension is very much influenced by the drag resistance of the yarn to the surrounding gaseous medium. While with lower production speeds the yarn tension depends substantially only on the delivery force, which is moreover absorbed by guide elements, such as godets for example, care must now be taken that the yarn tension for the greater realizable preorientation at these higher speeds, even without guide elements, will not exceed permissible values for the proper formation of perfect bobbins even if the path between the nozzles and the location of the bobbin or of yarn deposit, respectively, is long.
German Offenlegungsschrift [Laid-Open Application] No. 2,347,801 teaches a technique for winding yarns without godets at speeds of more than 2,500 m/min by grouping the individual filaments into a bundle or bundles beyond the cooling path and for providing them with a preparation coating. Since the outer surface of the yarn thus has much less drag resistance to the surrounding gaseous medium, no undesirably high yarn tension can develop.
German Offenlegungsschrift [Laid-Open Application] No. 2,530,618 discloses a procedure based on the same principle in that the yarn tension is reduced by grouping the filaments into bundles soon after they leave the spinning nozzles and then subjecting the bundles to a preparation treatment.